The influence of forest harvesting intensities on species and structural diversity of forests

To analyse influences of harvesting intensities on structural and species diversity of forests, an index wasdeveloped to quantify forest structural diversity on basis of the second and third National Forest Inventory of Germany for the state of Baden-Württemberg. This index (FSI = Forest Structure Index) includes 11 different aspects of forest structure. It was calculated for all sampling plots in Baden-Württemberg for two inventories and then aggregated for different types of forests (National Forest Inventories = NFI2002 and NFI2012). Almost all analysed types of forests showed an increase of the FSI for the inventory-period 2002 – 2012.

In a second step it was tested, if the FSI and the individual aspects of structural diversity were suitable to assess habitat quality of forest dwelling species. Therefore, we analysed how the variation of the FSI can explain prevalence of different taxonomic groups (TGs). This analysis was performed with data of the German Biodiversity Exploratories, providing information on many taxonomic groups (for example birds, bats, different groups of insects, vascular plants, fungi) as well as data on structural diversity of forests in three regions of Germany. The main aim of this step was to analyse the possibility to monitor taxonomic diversity by using structural elements to conclude on potential for biodiversity in a comprehensive way. Our results show that the variation in some taxonomic groups (e.g. the group of birds or deadwood fungi) can be explained by the FSI over different types of forests and regions in Germany.

In a last step, influences of different harvesting intensities on changes in structural diversity of forests were analysed. Based on these results, theoretical potentials of additionally harvestable woody biomass without affecting structural diversity were calculated for different types of forests. Our results indicate that especially middle-aged, conifer-dominated forest stands can be harvested more intensely before a reduction in structural diversity and biodiversity sets in.